Prop question

[Bill Ptaszynski]

Does anyone know where I can find out what prop came on my boat originally, my local dealer doesn't seem to be able to help(too old). I have a 1985 268DA with an Alpha 1 and 350 Merc. My top rpm is limited to 3200 and it seems to labor pretty hard, everything else checks good, full throttle at carb and linkage. I am going to pull the one thats on it off this weekend to check the pitch/cup.

Thanks,
Bill

 

[Matt89GT]

I would start with a 16x15P, 16 is the largest diameter prop that will work with with your Alpha and my reason for the 15 pitch is your only getting 3200 RPMS's when the engine should turn 4800, there are alot of problems that can contribute to lugging a engine besides the prop.

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[Bill Ptaszynski]

Thanks, yea everything else has been checked and is working fine. Not sure of the prop that is on it now, I did see the other thread about prop sizes/pitch. I am going to try an aluminum prop 15.25*15 (borrow) and see where my RPM's end up......